In one type of conventional image forming apparatus, images are formed using a color material that changes its properties by, for example, heating so that objects printed with the color material can be made invisible. In such an image forming apparatus, an ordinary multi function peripheral (MFP) is used in a printing process. When the MFP is of the electrophotographic type, a decolorable toner is used. In such a case, an erasing apparatus is provided separately from the MFP to change the properties of the toner. Printed paper mediums are heated using the erasing apparatus to erase the printed objects, so that the paper mediums can be reused.
When an electronic document file is printed on a printing medium such as a sheet of paper, identification information such as a QR code (registered trademark) or a barcode used as a trace ID of information may be printed on the printing side of the medium. When the printed medium used as an original document is copied, the identification information is analyzed in a scanning step to identify the document, and updated identification information is printed on each copy in a printing step. In this manner, the information of each copy can be traced without using expensive special sheets of paper.
The image forming apparatus for performing printing on mediums and the erasing apparatus can be designed so as to systematically communicate with each other. In this case, a combination of the above techniques allows the contents of a document to be erased to be judged by analyzing identification information on the document. More specifically, when the contents of the document are printed on a medium with, for example, a decolorable toner, the identification information used as a trace ID is printed with the decolorable toner used for the document or an ordinary toner so that the contents of the document can be judged. In this manner, the traceability of the document can be managed, and information about the version, secrecy level, etc. of the contents of the document can thereby be appropriately grasped.